Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $38.49   12.433%   $43.2755   $43.28   $43.30   $43.30  
  Purchase #2 $110.73   9.144%   $120.8552   $120.86   $120.85   $120.90  
  Purchase #3 $57.57   13.796%   $65.5124   $65.51   $65.50   $65.50  
  Purchase #4 $246.94   6.407%   $262.7614   $262.76   $262.75   $262.80  
  Purchase #5 $194.48   13.223%   $220.1961   $220.20   $220.20   $220.20  
  Purchase #6 $114.67   9.521%   $125.5877   $125.59   $125.60   $125.60  
  Purchase #7 $70.77   9.123%   $77.2263   $77.23   $77.25   $77.20  
  7 purchase totals = $833.65       $915.4146   $915.43   $915.45   $915.50